The present invention relates to a method of fabricating a three-dimensional structure by using an inkjet system to deposit droplets of a curable ink and build up the ink in layers. The invention also relates to a method of manufacturing a substrate having a spacer thereon using such a three-dimensional structure fabricating method.
One way to fabricate three-dimensional structures involves, by means of an inkjet system, delivering as droplets (such as by ejection) an ink having curability (referred to below simply as “ink”), causing the ink droplets to land in a predetermined pattern on a substrate and curing the deposited ink so as to form a layer of cured ink, then causing droplets of ink to be delivered and land on the resulting layer in a different predetermined pattern and curing the freshly deposited ink so as to create a different layer. By repeating these operations, a three-dimensional structure built up from layers of cured ink is created.
For example, JP 2005-205670 A discloses a three-dimensional object-forming apparatus having an ink head which ejects a UV-curable ink onto a smooth-surfaced member serving as a reference plane, a laser head which irradiates the UV-curable ink ejected from the ink head with a beam of ultraviolet light and thereby cures the ink, and a controlling means which carries out control by moving the ink head, the laser head and the smooth-surfaced member so as to build up layers of the ink on the smooth-surfaced member.
The three-dimensional structure-forming apparatus disclosed in JP 2005-205670 A is described as adjusting the dispersion of the ink and the thickness of the ink film by both adjusting the interval between the ink head and the laser head and also adjusting the period of time from when the UV-curable ink is ejected until laser irradiation is begun.
JP 2005-66530 A discloses a patterning apparatus which ejects droplets of liquid from nozzle orifices at a given period and irradiates the ejected droplets with pulsed light at times other than the period of time from just before to just after other droplets are ejected from the nozzle orifices. Providing a patterning apparatus with such a configuration is described as making it possible to form patterns having a high aspect ratio without a loss in adhesion, while at the same time preventing the nozzle orifices from clogging.
JP 2001-83528 A discloses a method of manufacturing liquid-crystal devices, which method includes a spacer-forming step in which a spacer-forming material is furnished a plurality of times in discrete portions to the same places on a substrate and cured so as to form spacers which define an interval between a pair of substrates.
JP 2001-83528 A mentions that the required height of the spacer can be more easily achieved by having the amount of the spacer-forming material furnished the second and subsequent times be smaller than the amount of material furnished the first time.
Here, in a method of fabricating a three-dimensional structure by using an inkjet system to deposit droplets of ink, cure the ink so as to form a layer, and thereby build up successive layers of ink, depending on the properties of the ink (e.g., wetting ability) when it lands, a droplet of ink that has just landed may spread while the ink is wet, as a result of which the ink that has landed may protrude beyond the cured ink in the underlying layer.
To resolve this, the method described in JP 2005-205670 A adjusts the time when laser irradiation is carried out after the ink has landed, thereby adjusting ink spread while the ink is wet. By thus curing the ink within a fixed period of time after the ink has landed, the ink can be prevented from spreading while wet. Moreover, curing the ink immediately after it lands enables the film thickness to be increased; that is, the ink that has landed can be cured in a high aspect ratio state.
The method described in JP 2005-66530 A irradiates ink droplets that have been ejected from the nozzles and are in flight with pulsed light, thereby initiating the curing process as the droplets fall. This makes it possible to have the droplets land after attaining a higher viscosity, and enables curing to be effected in a high aspect ratio state.
However, the method of JP 2005-205670 A requires that laser irradiation be carried out within a short, fixed period of time after the ink has landed, whereas the method of JP 2005-66530 A requires that light irradiation be carried out during the time from when the ink is ejected until immediately after it lands.
As a result, the ink head and the light irradiating means must be placed in close proximity to each other, which limits the degree of freedom allowed of the apparatus and the method.
Moreover, because the light to effect curing is irradiated at a position which is close to the ink head, even if the irradiation timing is adjusted as described in JP 2005-66530 A, there is a possibility that nozzle clogging will arise when irradiation is repeatedly carried out.
Furthermore, although wet spreading of the ink can be prevented by gradually decreasing the liquid volume of the ink that is ejected as described in JP 2001-83528 A, there are limits to the size of the three-dimensional structure that can be formed in this way. Moreover, because the liquid volume is gradually decreased, the ink must be ejected a large number of times in order to form a high three-dimensional structure, which lowers the productivity.